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— We certainly agree with Dr Fenton that the criterion of six months of illness adds considerably to the predictive power of the DSM-III definition, and presumably the Feighner definition, of schizophrenia. As we stated in the article that Dr Fenton's letter addresses: "It is clear that [the requirement of six months of illness] is the main predictor of the measures we have included under general outcome...." However, we hesitate to jump to the conclusion that "... for both definitions predictive validity derives only from the six-month duration requirement." The key may well be a combination of the psychotic phenomena specified by these two definitions and some duration of illness, which, as we suggested, may be less than six months. Fortunately, there is no need to jump to conclusions at all since this is an empirical question and a study currently under way by us may help to provide the answer.
Helzer JE, Brockington IF, Kendell RE. Definitions of Schizophrenia-Reply. Arch Gen Psychiatry. 1982;39(3):357. doi:10.1001/archpsyc.1982.04290030085019